The present invention relates to optical memory, and more specifically, to systems and methods for reading information bits with a spatially entangled state of light, more specifically, using a single photon in a uniform coherent superposition of being present in multiple spatial locations.
Optically encoded media such as optical discs, optical memory and barcodes are ubiquitous. The surface of an optical disc, for example, contains a long spiral track of data, along which, there are flat reflective areas called land and non-reflective pits (also called bumps). A flat reflective area represents a binary 1, while a non-reflective bump represents a binary 0. The optical reader drive shines a laser at the surface of the optical disc. Pits and lands have the same light-reflecting surface, but pits reflect the read-laser's light in a diffuse way and thus look relatively dark compared to the land areas. The photocurrent of the detector tracks the intensity profile of the reflected light that is captured by the entrance pupil of the optical pickup. The drive converts this photocurrent into 1s and 0s by signal processing, to read digital data from the disc.
Fundamentally, performance of any optical communication or imaging system is limited by noise of quantum-mechanical origin, and optical reading of a coded memory is no exception. In order to understand the ultimate performance bounds of an optical imaging system that is limited only by the laws of quantum physics, an analysis within a full quantum mechanical framework is indispensable. However, currently there remains a gap between achievable limits with classical and quantum transceivers.